Why did Frederick William conclude an armistice with Sweden early in his reign?

When Frederick William succeeded his father as elector of Brandenburg in December 1640, he inherited a territory that was ravaged and occupied by foreign troops. Lacking political experience and military strength, he initially pursued a policy of cautious neutrality to escape the intense pressure exerted by rival powers.1

By concluding an armistice with Sweden and discharging the Brandenburg troops that had been serving the Habsburgs, Frederick William sought to protect his domain from further devastation during the ongoing Thirty Years’ War. This strategic decision allowed him to distance his lands from the conflict and focus on the early years of reconstruction.1